October 1959, replacing US 24A signage in the Monroe area, after the state waited for final approval of the numbering system to be used in the state. In November 1960, sections of freeway opened from Indian River north to the southern Mackinac Bridge approaches in Mackinaw City and from St. Ignace to Evergreen Shores, and by December, the section of freeway running between Evergreen Shores and M-123 was scheduled to open. In 1961, the MSHD had proposed that the section of I-75 south of Detroit to Toledo be built as an electronic highway under a bid through General Motors; the testing for such a roadway was ultimately done at Ohio State University instead. That same year the original Zilwaukee Bridge, a bascule bridge across the Saginaw River was opened, along with a section of freeway north to Kawkawlin. In October 1961, the first segment of I-75 near Grayling opened, connecting M-18 with the city. By the end of the year, the freeway was completed between Kinross and Dafter in the UP, and the former segment of US 27 between Grayling and Gaylord was turned back to local control. After this individual segment of freeway was completed, it left a gap between Gaylord and Indian River that was designated "To I-75" on maps for the former segment of US 27, and US 27 was truncated to about south of Grayling. The section of I-75 was opened between Gaylord and Waters in July 1962. Another temporary To I-75 designation was applied along US 10 and US 27 from Bay City to Grayling. In August, the section between Gaylord and Vanderbilt was completed. On October 25, the section of freeway from M-24 near Pontiac to the Flint area opened. Also late in the year, the freeway gap was filled in between Vanderbilt and Indian River. The International Bridge and its approaches opened in Sault Ste. Marie on October 31, 1962. The following year, a set of segments opened in the Detroit area. The freeway was extended south from Pontiac to 11 Mile Road with a connection along M-150 to M-102 (8 Mile Road). Another section opened to connect with US 24 (Telegraph Road) in the Woodhaven area; a To I-75 designation was added to connect along US 24 and M-102 to M-150. On the other end of the state, the gaps in the freeway across the UP were completed in 1963 as well,